Defect-Rich Quasi Two Dimensional Metal Oxides with Strong Ferromagnetism

非技术说明形成永久磁体或被磁体吸引的材料称为铁磁性材料。这种材料有很多用途，从数据存储到电力系统。然而，铁磁性是一种不寻常的性质，只出现在少数物质中，如铁、镍、钴及其合金，以及一些稀土材料。这个项目的目的是了解超薄的二维(2D)材料可以产生多强的铁磁性，这些材料在体积上不是磁性的。空位是由“缺失”的原子引起的一种缺陷，它似乎在稳定2D半导体的磁性方面起着至关重要的作用。研究人员将进行一项实验和理论相结合的研究，以确定这些纳米片中可能形成的空位浓度，并量化它们对磁性的影响。这项研究具有实现低维铁磁材料的潜力，具有广泛的应用前景，包括存储器件和量子计算。该项目为代表不足的少数族裔本科生提供研究经验的机会，并提供实验和计算材料研究方面的教育和培训。该项目丰富了信息学恶作剧，让本科生在数据科学和材料科学与工程的交界处从事研究。该研究项目和结果将被整合到对高中教师和学生的宣传中。该项目的目的是了解准二维(2D)过渡金属氧化物中大量阳离子空位浓度的形成和稳定机制，并证明通过尺寸限制和点缺陷工程可以在非铁磁氧化物中诱导出强铁磁性。这个项目基于一个重要的假设，即当阳离子空位的厚度减少到纳米级时，可以在氧化物中产生并稳定在高水平的阳离子空位，这反过来又给2D材料带来了强大的铁磁性。PI发现富锌空位的2D氧化锌纳米片的室温铁磁性增强了几个数量级。在离子层外延的作用下，强烈的协同耦合现象使氧化锌纳米片中的空位浓度稳定在30%以上。实验与理论相结合的研究项目包括三个具体的研究任务。任务1是一项理论研究，旨在了解2D氧化物晶格中大量阳离子空位浓度稳定及其相关的强铁磁性的基本机制。任务2是对氧化锌纳米片中锌空位演化和稳定机制的实验研究，以了解阳离子空位的形成和稳定机制与纳米厚度、表面和晶界的关系。在任务3中，将超薄纳米片阳离子空位引起的特殊磁性量化为CeO和MnO氧化物，分别揭示了空位有序贡献、阳离子空位和过渡金属磁矩耦合效应。该项目的成功为设计和合成一系列具有高磁化强度和多功能的新型铁磁性2D纳米材料带来了变革性的知识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical DescriptionMaterials that form permanent magnets or are attracted to magnets are called ferromagnetic. Such materials have many uses, ranging from data storage to power systems. However, ferromagnetism is an unusual property that occurs only in a few substances such as iron, nickel, cobalt and their alloys, and some rare earth materials. This project aims to understand how strong ferromagnetism can arise from ultrathin, two-dimensional (2D) materials, that are not magnetic in bulk form. Vacancies, a type of defect arising from “missing” atoms, appear to play a crucial role in stabilizing magnetism in 2D semiconductors. The investigators will perform a combined experimental and theoretical study to determine the concentration of vacancies that can be formed in these nanosheets and quantify how they impact magnetic properties. This research has the potential to realize low-dimensional ferromagnetic materials with a broad range of applications, including memory devices and quantum computing. This project offers opportunities to provide research experiences to underrepresented minority undergraduate and provides education and training on experimental and computation materials research. This project enriches the Informatics Skunkworks to engage undergraduates in research at the interface of data science and materials science and engineering. The research project and results will be integrated into outreach to high school teachers and students.Technical DescriptionThe objective of this project is to understand the formation and stabilization mechanisms of massive cation vacancy concentrations in quasi two-dimensional (2D) transition metal oxides and demonstrate that strong ferromagnetism can be induced in non-ferromagnetic oxides by dimension confinement and point defect engineering. This project is based on an overarching hypothesis that cation vacancies can be created and stabilized at a high level in oxides when their thickness is reduced to the nanometer level, which in turn introduces a strong ferromagnetism to the 2D material. The PIs discovered orders of magnitude enhancement of room temperature ferromagnetism from zinc vacancy-rich 2D ZnO nanosheets. A strong cooperative coupling phenomenon stabilized a vacancy concentration greater than 30% in ZnO nanosheets, enabled by ionic layer epitaxy. The combined experimental and theoretical research project consists of three specific research tasks. Task 1 is a theoretical study to understand the fundamental mechanisms of massive cation vacancy concentration stabilization and associated strong ferromagnetism in 2D oxide lattices. Task 2 is an experimental investigation of zinc vacancy evolution and stabilization mechanisms in ZnO nanosheets to understand the cation vacancy formation and stabilization mechanisms in correlation to the nanoscale thickness, surfaces and grain boundaries. In task 3, the extraordinary magnetic properties rising from the cation vacancies in ultrathin nanosheets are quantified in cerium and manganese oxides, as representative examples to reveal vacancy ordering contribution, and cation vacancy and transition metal moment coupling effects, respectively. Success of this project brings transformative knowledge for the design and synthesis of a new family of ferromagnetic 2D nanomaterials with high magnetization and multi-functionality.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.